So I finally learned what a "cush drive" is last night when I went to clean my rear wheel and the hub fell off.

What is the purpose of having a "cush drive"? It seems counter intuitive to have rubber in the drive line as it adds slop to the system. In cars we always try to take all the rubber out.

Why have it? Can it be replaced solid (such as aluminum spacers)? Advantages of having the rubber?

Chris

 

A cush drive is a part of a motorcycle drive-train that is designed to reduce stress from engine torque damaging other components during gear or throttle changes. A common design used by Honda, in particular on the VTR 1000F Superhawk is made of three major pieces: the wheel, the sprocket assembly, and the rubber damper. The wheel and the sprocket assembly fit together with five sections much like two hands woven together. In between the contact of the two assembly are rubber blocks. This makes it so the wheel and the sprocket have a dampening layer between them, and the rubber blocks reduce wear and fatigue of the metal assemblies.
When the rubber damper becomes old and hardens, or wears out, the changes in load on the drive chain instigated by changes in throttle position or changing gear can cause snatchiness in the power delivery. Loads particularly on the drive chain can be massively increased in these conditions, increasing the risk of breakage or of contact with the swinging arm resulting in damage. Perhaps more pointedly the sudden transfer of force to the rear tyre can cause momentary loss of traction (lock or spin) resulting in small changes of direction or at worst total loss of control.

 

HAHA...I read the Wikipedia answer already, I was looking for a bit more first hand point of view.

It just seems to me that rubber in the drivetrain isn't a good idea (from a performance standpoint).

 

ok well think of it almost like a limited slip rear end in a car as apose to like solid axles on a car set up for drag, without that rubber in there there isnt gunna be any smoothness to the power transfer up or downshifting it is goin to cause it to be very "jerky" i guess would be a good enough word to describe it, and the parts in there arent made for handling that kind of stress, so i guess if you wanted to rebuild the tranny replace both gears and the rear tire assembly with hardened materials you might not have a problem with breakage, just controlling the power, otherwise just put a new cush in there and put it back together, it was designed like that for a reason.

 

Performance-wise, I seriously doubt it is robbing any significant HP. Yeah, as the rubber is compressed heat is created, but most of the energy is only being stored/released. The porpose is to spread the load over time.

This, as stated, keeps things from sheering/breaking. It does it in both directions, engine>rear-end and rear-end>engine (think accelleration vs engine braking). Sudden loads tend to exaggerate/focus the energy (this is a bad thing on the molecular level).

Until somebody figures out how to create a material that is light-weight and can take a infinite load in micro-seconds, we have to engineer to mitigate these factors into the design of the drive-train. So, no, you don't want a solid connection at the rear (unless, maybe, you are only drag-racing). Cars have a much more robust drive-train, would be my guess, on why you can get away with more.

I want to point out that (by my observation) most of the folks here are 'twisty' track riders, not straight 1/4 milers. So if that's where you are heading with this, you might cast your net wider. Try hooking up with a drag focused forum, as well (not saying this is the wrong forum for you, mind you), they might have more drag specific answers. You may be on to something with your thesis, but not for street-riding.

Hope this helps, Ern

 

From the factory cars often have rubber bushings in the drive-shaft/U-joint mounts to dampen vibrations and remove shock, however those get ditched and replaced with aluminum spacers in performance applications.

I'm not going to ditch it (without an alternative and lots of information), I was just really surprised to find rubber there.

Thanks,
Chris

 

P.S.
I started an edit right after I posted. I scanned your post again, and noted I had mis-read your post. I had read it as "cars don't", not as, "it's removed". Doh!!

Anyway check my edit, and hopefully I won't appear quite as dumb. ;-)

Ern

 

HAHA... yeah.... can't count how many times I have made a reply, realized I misread, and frantically hit edit all the time praying to God that nobody reads my stupid post before I get it fixed...